1. Field of the Invention
The present invention relates to an image processing apparatus for printing an image by converting multi-value image data to binary data, and combining the printing or non-printing of dots. Particularly, the invention relates to image processing that correlates and prepares a dot-arrangement pattern, which indicates the printing/non-printing of dots, with multi-value image data, and effectively lessens image defects that are caused by the arrangement period of the dot-arrangement pattern.
2. Description of the Related Art
Many inkjet printers convert low-resolution multi-value image data (600 dpi, 256 values) to high-resolution binary data (1200, dpi, 2 values), and print an image by printing (1) or not printing (0) dots. When doing this, often the main image processing is performed using the original resolution and gradation of the image data, and then after quantizing the image data to that having lower gradation, a dot-arrangement pattern for which the printing/non-printing of dots is set in advance is often used to convert the image data to binary data that corresponds to the printing resolution. Preferably, a plurality of patterns in which the positions where the dots are arranged differ from each other even though the gradation is the same are prepared, and also, in order to make uniform the frequency of use of printing elements, preferably these plural patterns are used without bias.
For example, Japanese Patent Laid-Open No. 2004-090462 discloses a method where, in order to prevent stripes or the like that occur due to the periodic arrangement of the dot-arrangement pattern, prepares an A×B matrix in which the plural patterns above that correspond to the same gradation are arranged in the raster direction and column direction.
Moreover, Japanese Patent Laid-Open No. 2009-039944 discloses construction that prepares plural matrices in which the plural patterns above are arranged, and correlates those matrices with the conveyance amount that changes according to the printing mode.
In this way, by devising the arrangement method and arrangement size of the plural dot patterns, lessening image defects that are caused by the periodic arrangement of the dot-arrangement pattern can be expected.
Incidentally, it is preferred that the arrangement method and arrangement size of the plural dot patterns described above be such that, in order to obtain the optimum effect, the printing mode is different and optimized for each ink color, or in other words, for each nozzle array that discharges ink.
However, in recent years, as ink that is used has become multi-colored, and there is a diversification of dot sizes, there has been a tendency to increase the number of nozzle arrays that discharge ink. At the same time, in order to improve both image quality and printing speed, many printing modes having different numbers of nozzle arrays, printing resolutions, conveyance speeds and the like used in printing have been prepared for a single printer. In such a situation, when trying to prepare a fixed matrix that corresponds to each of the nozzle arrays in each printing mode as disclosed in Japanese Patent Laid-Open No. 2004-090462 and Japanese Patent Laid-Open No. 2009-039944, the increase in the needed memory capacity is a concern, and maintaining that memory capacity becomes a large problem.